It is often necessary to have a plurality of parallel compaction systems to sustain a required throughput data rate. Each encoder and decoder of the compaction device must process the data directed to it in a known maximum period of time. Since the compaction is done by a plurality of the parallel units, the slowest unit can limit the throughput data rate.
It is, therefore, an object of the present invention to provide a compaction system that can encode and decode the data in a known maximum period of time.
Each compaction unit processes multiple sets of the data, the modifier information obtained from each encoder must be retained across the sets of data. The order of the sets of data must also be kept the same throughout the process. The modifier data is obtained from the statistical tables of the arithmetic coding system. Also, for decoding, the modifier information obtained from each decoder must be retained across the sets of data. The standard method is to solve the modifier retention problem by including one statistics table in one compaction unit so that a specific format is achieved for a given data rate. The throughput data rate is then determined by the number of compression units that are placed in parallel. The larger the number of compression units, the higher the data rate can be since each unit can process a portion of the data. So the throughput required determines the number of parallel compaction units. The number of compaction units determines the format of the compressed data, since the learning curve of the statistic table with each encoder is used to process, i.e., compress, later data. More compaction units formerly added statistic tables and therefore changed the format. Earlier encoded media could no longer be reliably decoded. If a higher data rate is required at a later time, then a new format using more of the compaction units is established. The new format, that the higher number of parallel connected compaction units provides, prevents the decoding of the data that was encoded under the previous format and vice versa. Thus before this invention, the increase in the data rate precluded upward and downward compatibility between the previous system and the improved system.
It is, therefore, another object of the present invention to provide a compaction system through which a higher data rate can be obtained while retaining the same format for all systems.